Oven for glass article

ABSTRACT

An exhaust oven for heat treating and simultaneously evacuating cathode ray tubes includes a tunnel structure with a through passageway and temperature control apparatus for providing regulated heating and/or cooling of the atmosphere in one or more longitudinal zones of the passageway. The oven also includes apparatus for conveying the tubes along the passageway and exhaust ducts operatively connected to the necks of the tubes during conveyance to evacuate gases therefrom. Baffles within at least one of the zones of the passageway circulate the atmosphere about the exteriro of the tubes. The baffles include at least one inlet directing a flow of atmosphere to impinge onto the face of the screen panel of each tube and one or more outlets in adjacent spaced relationship to side edges of said panel and/or to the neck of the tube for exit of the flow of atmosphere from the baffles.

CROSS REFERENCE TO CO-PENDING APPLICATION

This patent application is a divisional application of U.S. patentapplication Ser. No. 08/952,631 filed Feb. 20, 1998, now U.S. Pat. No.6,015,288 granted Jan. 18, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ovens for the heat treatment of glass articlesand, more specifically, to tunnel type ovens for continuous treatment ofcathode ray tubes at the same time as gases contained within the tubeare evacuated, commonly referred to as “exhaust ovens”.

2. Description of the Related Art

One example of an exhaust oven for this purpose is described in U.S.Pat. No. 4,752,268.

The heating and cooling of the shaped glass envelope forming the tube tominimise stresses therein and its evacuation which subjects the walls tosubstantial external pressure is a critical operation. The demand forlarger and flatter cathode ray tubes, particularly for domestic highdefinition “flat screen” television receivers, has increased theprocessing problems and the need for ovens giving economical productionand minimum damage or wastage of these high value components.

The object of the invention is to provide an exhaust oven for cathoderay tubes which is particularly effective and reliable in operation toprovide economical and consistent production.

SUMMARY OF THE INVENTION

An exhaust oven for heat treating and simultaneously evacuating cathoderay tubes includes a tunnel structure with a through passageway andtemperature control apparatus for providing regulated heating and/orcooling of the atmosphere in one or more longitudinal zones of thepassageway. The oven also includes apparatus for conveying the tubesalong the passageway and exhaust ducts operatively connected to thenecks of the tubes during conveyance to evacuate gases therefrom.Baffles within at least one of the longitudinal zones of the passagewaycirculate the atmosphere about the exterior of the tubes. The bafflesinclude at least one inlet directing a flow of atmosphere to impingeonto the face of the screen panel of each tube and one or more outletsin adjacent spaced relationship to side edges of said panel and/or tothe neck of the tube for exit of the flow of atmosphere from thebaffles.

According to one aspect of the invention there is provided an exhaustoven for heat treating and simultaneously evacuating cathode ray tubesas defined by claim 1 of the appended claims.

According to another aspect the invention comprises a cathode ray tubeas defined by claim 10 hereof.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the invention is now more particularly described withreference to the accompanying drawings, wherein:

FIG. 1 is a lateral cross-section of a heating zone of a CRT exhaustoven,

FIG. 2 is a longitudinal section of part of said zone on line 2—2 ofFIG. 1, and

FIG. 3 is a diagrammatic plan view of the oven and its transport means.

DETAILED DESCRIPTION OF THE INVENTION

The exhaust oven comprises a tunnel structure 10 having outer structuralwalls 12 lined with insulating material 14 to define a through passage16 which is rectangular in lateral section.

Transport means comprises a track 18 having vertically spaced upper andlower guide rails 20. 22 immediately below and to one side of structure10 and extending in a continuous loop from the tunnel exit 24 round tothe tunnel entrance 25 (FIG. 3). There are loading and unloadingstations 28, 30 along the part of track 18 outside structure 10.

A train of vacuum carts 32 runs on track 18, each cart being providedwith an upwardly projecting support 34 which projects into the bottompart of passage 16 through a longitudinal slot 36 in the floor ofstructure 10. Each support 34 incorporates an exhaust duct and isoperatively connected to the neck 38 of the glass envelope of a cathoderay tube (CRT) 40 so that the latter is transported along passage 16 bymovement of the cart with its large area screen panel 42 directedupwards and maintained generally centrally of the passage lower halfsubstantially spaced from its walls. Each tube is further supported andlocated by a respective cage 44.

During transport through the oven, vacuum carts 32 are operatedautomatically in known manner to exhaust the interior of each CRT 40.The CRTs for processing are mounted on the carts 32 at the loadingstation 28 and are dismounted after processing at the unloading station30.

As well as being exhausted the CRTs 40 are heat treated within the oven,for example in three main stages by passage through successive zones A,B and C (FIG. 3) though there may be more or less than three zones andthe treatment sequence may vary according to requirements. Typically thefirst zone A is a heating zone raising the temperature of the CRT toanneal and relieve stresses in the envelope followed by a first coolingzone B in which the temperature is reduced in a controlled manner andending with a final cooling zone C for further temperature reduction.

Each CRT 40 travels in a respective said cage 44-for protection and safesupport but without any substantial restriction in airflow to and fromthe exterior of the tube envelope itself.

The arrangement for applying heat to the CRTs in zone A will now bedescribed in detail referring in particular to FIG. 1. Fixed bafflemeans 50 within and spaced from the walls of structure 10 form an innerlongitudinal enclosure surrounding but spaced from cages 44 as they andCRTs 40 travel therethrough. The floor 52 of enclosure 50 defines acontinuous central slot 54 just wide enough to allow passage of thesupports 34, and the roof 56 thereof defines circular inlet openings 58(one only shown) spaced at longitudinal intervals and each provided witha motor driven fan impeller 60 for driving a flow of air downwardly intothe enclosure.

A diffusion screen or other distributor device 61 may be provided in theupper region of baffle means 50 between the roof and the tops of cages44.

Each side wall 62, 64 of enclosure 50 defines outlet openings 66, 68 atintervals along its length, these openings being fitted with dampers orother means of adjusting their effective aperture and/or effectivevertical or other positioning in the respective side wall.

Outlet openings 66 are set to be substantially on a level with the sideedges of panels 42 of the CRTs 40, i.e. closely adjacent to the widestpart of the tube envelope.

The space between the outside of enclosure 50 and the inner faces of theinsulation 14 lining the walls of structure 10 forms a circulationpassage for distribution of heated air out of contact with the CRTs 40.Heating means, for example gas fueled radiant tube heaters 17, indicateddiagrammatically in FIG. 1, automatically regulated in known manner heatthe circulating air to the required temperature.

In operation the hot air is driven in a downflow by fan impeller 60 intoenclosure 50 so that it impinges directly on the large area upwardlydirected face of panel 42 of the tube envelope, spreading thereover asindicated by the arrows in FIG. 1 to flow round its edges so that it isevenly heated. A substantial proportion of the flow is drawn from theregions of the side edges of the panel to exit through outlet openings66,68. A small proportion of the flow passes downwardly towards the neckof the tube so that this part of the envelope, which is particularlyliable to failure, is more gently heated. This further downflow is drawnthrough slot 54 to recirculate around the outside of enclosure 50 underthe action of the fan impellers 60. Surplus heated air is drawn off byexhaust ducts 72 extending through the side walls of tunnel structure10.

The air flow around the tube envelope can be selectively controlled andregulated within close tolerances by monitoring and controlling theheating temperature. regulating the speed and hence throughput of thefan impeller 60, and adjustment of the dampers or other controls of theoutlet opening 66,68. Adjustments will be made to suit the particularsize and shape of CRT being processed.

It will be appreciated that various arrangements for heating the airflow and for its effective recirculation minimizing heat losses forgreatest efficiency can be provided, for example surplus hot air passingat a lower temperature from zone A could be applied in zone B to effectfirst stage cooling with or without mixing with cold air depending onthe temperature gradient required.

It is to be understood that the described air circulation andapplication in zone A may also be used in one or more of the succeedingzones B and/or C for providing the desired temperature gradient throughthe exhaust oven.

The use of the invention ensures even temperature distribution asapplied to the glass envelopes of the CRTs throughout the processingcycle so that the thermal gradients within the glass are minimized toreduce risk of failure even though the glass is being subjected toadditional stresses from the exhausting process. The apparatus isapplicable to the processing of CRTs of all types but is believed to beparticularly advantageous for the large volume processing of the largersizes of “flat screen” CRTs needed for televisions and computermonitors.

What is claimed is:
 1. An exhaust oven for hear treating andsimultaneously evacuating cathode ray tubes (40), said oven comprising atunnel structure (10) defining a through passage, temperature controlmeans for providing regulated heating and cooling of the atmospherecontained in one or more longitudinal zones of the passage, transportmeans (32) for conveying the tubes along said passage and includingexhaust ducts operatively connected to the necks (38) of the cubesduring conveyance to evacuate gases therefrom, and baffle means (50)within at least one said zone of the passage for circulating saidatmosphere about the exterior of the tubes; characterized in that thebaffle means includes at least one inlet formation (58) directing a flowof atmosphere to impinge onto the large area face of the screen panel(42) of each tube in use, and one or more outlet formations (66,68,54)in adjacent spaced acting relationship to side edges of said panel andto the neck of the tube for exit of said flow from the baffle means. 2.An oven for heat treating cathode ray tubes in a plurality of zones,said oven comprising: a tunnel structure having outer walls defining athrough passage; heaters for heating the atmosphere in at least one zoneof said oven to a desired temperature; and a baffle structure within theat least one zone for circulating the atmosphere about the exterior ofthe tube, said baffle structure defining at least one inlet opening fordirecting a flow of atmosphere to impinge onto a screen panel of thetube, and at least one outlet opening in the outer walls of said tunnelstructure for allowing the flow of atmosphere to exit from said bafflestructure.
 3. The oven according to claim 2 further comprising a slotfor recirculating the atmosphere around said baffle structure.
 4. Anoven for thermally treating a cathode ray tube, said oven comprising: atunnel structure defining outer walls; a baffle having at least oneinlet opening located in a top portion of said baffle for directing aflow of atmosphere downward onto a screen panel of the tube, and atleast one outlet opening through the outer walls of said tunnelstructure adjacent the screen panel of the tube for directing the flowof atmosphere from said baffle; and means for heating and cooling theflow of atmosphere within said oven.
 5. An exhaust oven for heattreating and simultaneously evacuating cathode ray tubes (40), said ovencomprising a tunnel structure (10) defining a through passage,temperature control means for providing regulated heating of theatmosphere contained in one or more longitudinal zones of the passage,transport means (32) for conveying the tubes along said passage andincluding exhaust ducts operatively connected to the necks (38) of thetubes during conveyance to evacuate gases therefrom, and baffle means(50) within at least one said zone of the passage for circulating saidatmosphere about the exterior of the tubes; characterized in that thebaffle means includes at least one inlet formation (58) directing a flowof atmosphere to impinge onto the large area face of the screen panel(42) of each tube in use, and one or more outlet formations (66, 68, 54)in adjacent spaced acting relationship to side edges of said panel or tothe neck of the tube for exit of said flow from the baffle means.
 6. Anoven for heat treating cathode ray tubes in a plurality of zones, saidoven comprising: a tunnel structure having outer walls defining athrough passage; heaters for heating the atmosphere in at least one zoneof said oven to a desired temperature; a baffle structure within the atleast one zone for circulating the atmosphere about the exterior of thetube, said baffle structure defining at least one inlet opening fordirecting a flow of atmosphere to impinge onto a screen panel of thetube, and at least one outlet opening in the outer walls of said tunnelstructure for allowing the flow of atmosphere to exit from said bafflestructure; and a train of carts driven through the passage in acontinuous loop with loading and unloading stations outside the tunnelstructure for mounting and removing the cathode ray tubes.
 7. An ovenfor heat treating cathode ray tubes in a plurality of zones, said ovencomprising: a tunnel structure having outer walls defining a throughpassage; heaters for heating the atmosphere in at least one zone of saidoven to a desired temperature; and a baffle structure within the atleast one zone for circulating the atmosphere about the exterior of thetube, said baffle structure defining at least one inlet opening fordirecting a flow of atmosphere to impinge onto a screen panel of thetube, and at least one outlet opening in the outer walls of said tunnelstructure for allowing the flow of atmosphere to exit from said bafflestructure, wherein said heaters are disposed in a circulation passage.8. An oven for heat treating cathode ray tubes in a plurality of zones,said oven comprising: a tunnel structure having outer walls defining athrough passage; heaters for heating the atmosphere in at least one zoneof said oven to a desired temperature; a baffle structure within the atleast one zone for circulating the atmosphere about the exterior of thetube, said baffle structure defining at least one inlet opening fordirecting a flow of atmosphere to impinge onto a screen panel of thetube, and at least one outlet opening in the outer walls of said tunnelstructure for allowing the flow of atmosphere to exit from said bafflestructure, and a fan impeller for directing the atmosphere onto faces ofthe cathode ray tubes.